Control of exposure of camera

ABSTRACT

A device for controlling exposure of a camera is provided. An image of an area ahead of a vehicle is acquired by a camera provided in the vehicle. A traveling speed of the vehicle is acquired. An exposure area in the acquired image is set by a setting section, in which the exposure area is used for exposure control of the camera. By a calculating section, a control value for performing the exposure control is calculated based on pixel values of pixels included in the exposure area. The setting section changes a size of the exposure area based on the traveling speed, such that, when the traveling speed is a first speed, the size of the exposure area in the acquired image is smaller compared to that when the traveling speed is a second speed that is lower than the first speed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority fromearlier Japanese Patent Application No. 2013-10417 filed Jan. 23, 2013,the description of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to controlling exposure control of acamera based on images captured by the camera, and in particular, tocontrolling the exposure of a camera mounted in a vehicle.

2. Description of the Related Art

A technology is known in which exposure control of a camera that isinstalled in a vehicle is performed based on an image captured by thecamera. For example, JP-A-2010-041668 discloses a technology in which acamera captures an image at an initial exposure. An adaptive exposure isthen set based on the image captured at the initial exposure.

Specifically, a plurality of areas for exposure control are set inadvance in the image captured at the initial exposure. An averageluminance is detected for each of the areas. For each area, whether ornot the area is an area (unsuitable area) in which edge components areassumed to be undetectable is judged based on the average luminance ofthe area. The edge components are undetectable due to excessive orinsufficient exposure. When judged that any of the areas is anunsuitable area, the exposure of the camera is set to the adaptiveexposure. The adaptive exposure is based on the average luminance of theunsuitable area.

As described above, a technology is known in which exposure control of acamera is performed based on the average luminance of an area forexposure control that is set in advance in an image captured by thecamera. However, the appropriate manner of determining the area forexposure control in the captured image may differ depending on travelconditions of the vehicle and the like.

SUMMARY

Hence, it is desired to provide a technology for setting an area forexposure control depending on travel conditions of a vehicle.

An exposure control device according to an exemplary embodiment includesan image acquiring means, a speed acquiring means, a setting means, anda calculating means.

The image acquiring means acquires an image of an area ahead of avehicle that is captured by a camera. The speed acquiring means acquiresa traveling speed of the vehicle. The setting means sets an exposurearea that is an area used for exposure control in the captured image.The calculating means calculates a control value for performing exposurecontrol of the camera, based on pixel values of pixels included in theexposure area.

Specifically, the setting means changes a size of the exposure area inthe captured image based on the traveling speed, such that, when thetraveling speed is a first speed, the size of the exposure area in thecaptured image is smaller compared to that when the traveling speed is asecond speed that is lower than the first speed.

As a result of the above-described configuration, an exposure areahaving a size suitable for the traveling speed of the vehicle can beset. In other words, a collision margin time TTC (time-to-collision)becomes shorter as the traveling speed increases. The collision margintime TTC refers to the amount of time until collision with an obstacle,when the vehicle travels while maintaining a certain traveling speed. Inother words, with reference to a certain collision margin time TTC, thedistance to the subject obstacle becomes farther as the traveling speedincreases. Therefore, in a situation in which the traveling speed ishigh, compared to a situation in which the traveling speed is low,importance is required to be placed on detection of a target at a fardistance. In the present embodiment, the exposure area in the capturedimage is set to a smaller size when the traveling speed is higher.Therefore, importance can be placed on detection of targets at fardistances.

Reference numbers in the parentheses in this section and the scope ofclaims indicate an example of correlation with the specific meansdescribed in an embodiment, described hereafter. The references numbersdo not limit the technical scope of the present embodiment.

In addition, the present embodiment can be actualized as various aspectsin addition to the above-described exposure control device. For example,the present embodiment can be actualized as a vehicle control system inwhich the exposure control device is a constituent element, a programenabling a computer to function as the exposure control device, arecording medium on which the program is recorded, or an exposurecontrol method.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram of a configuration of a vehicle controlsystem;

FIG. 2 is a flowchart (1) of an exposure control process;

FIG. 3 is a flowchart (2) of the exposure control process;

FIG. 4 is a diagram of exposure areas based on traveling speed in acaptured image;

FIG. 5 is a diagram of exposure areas based on steering angle in acaptured image;

FIG. 6 is a diagram of exposure areas based on pitch angle in a capturedimage;

FIG. 7 is a diagram of target areas in a captured image;

FIG. 8 is a diagram of an exposure area that is expanded to include apartially overlapping target area;

FIG. 9 is a diagram of an exposure area that is expanded to include atarget area approaching the exposure area;

FIG. 10 is a graph of collision margin time TTC; and

FIG. 11 is a diagram of a selection method for selecting a plurality oftargets based on order of priority.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment to which the present invention is applied will hereinafterbe described with reference to the drawings.

1. Configuration

A vehicle control system 1 shown in FIG. 1 is mounted in a vehicle VE.The vehicle control system 1 includes a camera 11, a vehicle speedsensor 12, a steering angle sensor 13, a gyro sensor 14, a cameracontrol section 15, a vehicle control section 16, a notifying section17, a brake control section 18, and an engine control section 19.

In the vehicle control system 1, the camera control section 15 iscapable of communicating with the camera 11, the vehicle speed sensor12, the steering angle sensor 13, the gyro sensor 14, and the vehiclecontrol section 16. In addition, in the vehicle control system 1, thevehicle control section 16 is capable of communicating with the cameracontrol section 15, the notifying section 17, the brake control section18, and the engine control section 19. The means for actualizingcommunication between constituent elements in the vehicle control system1 is not particularly limited.

The camera 11 is attached such as to capture an image of an area aheadof an own vehicle VE (the vehicle in which the vehicle control system 1is mounted) from the center of the front side of the own vehicle VE. Thecamera 11 transmits image data (captured images of the area ahead of theown vehicle VE) to the camera control section 15.

The vehicle speed sensor 12 transmits detection information (informationindicating the vehicle speed at the time of detection) to the cameracontrol section 15.

The steering angle sensor 13 detects a steering angle of a steeringwheel of the own vehicle VE. The steering angle sensor 13 transmitsdetection information (information indicating the steering angle at thetime of detection) to the camera control section 15.

The gyro sensor 14 detects a pitch angle (road gradient of a road onwhich the own vehicle VE is traveling). The pitch angle indicates a tiltin a front/back direction of the own vehicle VE in relation to ahorizontal plane. The gyro sensor 14 transmits detection information(information related to the pitch angle at the time of detection) to thecamera control section 15.

The camera control section 15 is an electronic control device thatperforms exposure control of the camera 11, target detection based on animage captured by the camera 11, and the like. The camera controlsection 15 includes a central processing unit (CPU), a read-only memory(ROM), a random access memory (RAM), and the like.

The vehicle control section 16 is an electronic control device thatperforms vehicle control, such as notification control, brake control,and engine control. The vehicle control section 16 includes a CPU, aROM, a RAM, and the like.

The notifying section 17 performs notification to a driver of the ownvehicle VE using sound, light, and the like when a warning signal isreceived from the vehicle control section 16.

The brake control section 18 is an electronic control device thatcontrols braking of the own vehicle VE. The brake control section 18includes a CPU, a ROM, a RAM, and the like. Specifically, the brakecontrol section 18 controls a brake ACT based on a detection value froma sensor. The sensor detects a pressing amount of a brake pedal. Thebrake ACT is an actuator that opens and closes a pressure-increasecontrol valve and a pressure-decrease control valve that are provided ina brake hydraulic circuit. In addition, the brake control section 18controls the brake ACT such as to increase the braking force of the ownvehicle VE in adherence to an instruction from the vehicle controlsection 16.

The engine control section 19 is an electronic control device thatcontrols start/stop of an engine, fuel injection amount, ignitiontiming, and the like. The engine control section 19 includes a CPU, aROM, a RAM, and the like. Specifically, the engine control section 19controls a throttle ACT based on detection values from a sensor. Thesensor detects a pressing amount of an accelerator pedal. The throttleACT is an actuator that opens and closes a throttle that is provided inan intake pipe. In addition, the engine control section 19 controls thethrottle ACT such as to reduce driving force of an internal combustionengine in adherence to an instruction from the vehicle control section16.

2. Processes

Next, a method for controlling exposure of the camera 11 performed bythe camera control section 15 will be described. The camera controlsection 15 has a storage section (such as a ROM). The storage sectionstores therein an exposure control program for actualizing exposurecontrol of the camera 11. The camera control section 15 (specificallythe CPU) performs an exposure control process based on the exposurecontrol program. The exposure control process will hereinafter bedescribed with reference to the flowcharts in FIG. 2 and FIG. 3. Thestart of the exposure control process shown in FIG. 2 and FIG. 3 istriggered by the start of the engine of the own vehicle.

First, the camera control section 15 acquires image data (a capturedimage of the area ahead of the own vehicle) from the camera 11 (stepS101).

Then, the camera control section 15 acquires respective detectioninformation (traveling speed, steering angle, and pitch angle of the ownvehicle) from the vehicle speed sensor 12, the steering angle sensor 13,and the gyro sensor 14 (step S102).

Next, the camera control section 15 sets an exposure area in thecaptured image acquired at step S101 (step S103). The exposure area isan area used for exposure control. Examples of an exposure area in acaptured image are shown in FIG. 4. FIG. 4 shows three exposure areasE1, E2, and E3. The exposure area E1 (the area enclosed by dotted lines)has a first size. The exposure area E1 is a rectangular area having thelargest size. In the example in FIG. 4, the exposure area E1 occupiesthe overall lower area of the captured image. The exposure area E2 has asecond size (the area enclosed by dashed lines). The exposure area E2 isa rectangular area that is smaller than the exposure area E1 having thefirst size. In the example in FIG. 4, the exposure area E2 is includedin the exposure area E1. The exposure area E3 has a third size (the areaenclosed by double-dot chain lines). The exposure area E3 is arectangular area that is smaller than the exposure area E2 having thesecond size. In the example in FIG. 4, the exposure area E3 is includedin the exposure area E2. In FIG. 4, the three exposure areas E1, E2, andE3 are shown in a single captured image to facilitate comparisons ofsize and position. However, the three exposure areas E1, E2, and E3 arenot set at the same time, but rather, are selectively set.

Specifically, the size and the position of the exposure area in thecaptured image change based on the traveling speed, the steering angle,and a change amount Δθ of the pitch angle of the own vehicle.

First, as a reference position of the exposure area, a position in astate in which the steering angle and the change amount Δθ of the pitchangle are 0 degrees will be described. In a state in which the steeringangle is 0 degrees, the steering wheel is not operated in either theleftward or rightward direction (straight-ahead traveling state). Inaddition, in a state in which the change amount Δθ of the pitch angle is0 degrees, for example, the tilt in the front/back direction of the ownvehicle (the road gradient of the road on which the own vehicle istraveling) is 0 degrees. In other words, the own vehicle is in a levelstate. However, this is not limited thereto. For example, in an instancein which the own vehicle and a leading vehicle are present on a slopehaving the same tilt, the pitch angle of the slope may serve asreference.

As shown in FIG. 4, the position of the exposure area in a state inwhich the steering angle and the change amount Δθ of the pitch angle are0 degrees is set to a position in which a focus of expansion (FOE) ofthe camera 11 is at the center of the upper side of the rectangle. Thesize of the exposure area is selected based on the traveling speed.

Specifically, for example, when the traveling speed is 0 or greater andless than V1, the exposure area E1 having the first size is selected.When the traveling speed is V1 or greater and less than V2 (V1<V2), theexposure area E2 having the second size is selected. When the travelingspeed is V2 or greater, the exposure area E3 having the third size isselected. In other words, the size of the exposure area is set to becomesmaller as the traveling speed increases. In other words, as thetraveling speed increases, detection at a position away from the ownvehicle becomes important. Here, an example is given in which the sizeof the exposure area is changed between three stages. However, this isnot limited thereto. The size of the exposure area may be changedbetween two stages, or four or more stages.

Next, the position of the exposure area in a lateral direction in thecaptured image based on the steering angle will be described. As shownin FIG. 5, when the steering angle increases to the left side (thedirection for turning left), the position of the exposure area in thelateral direction in the captured image (FIG. 5 shows exposure areas E2Land so E3L) is shifted to the left side in relation to the referenceposition (the exposure areas E2 and E3 in FIG. 4; indicated by finelines in FIG. 5). In the example in FIG. 5, the exposure area E2L isshifted to the left side in relation to the exposure area E2 that is inthe reference position. The exposure area E3L is shifted to the leftside in relation to the exposure area E3 that is in the referenceposition. On the other hand, when the steering angle increases to theright side (the direction for turning right), the position of theexposure area in the lateral direction in the captured image shifts tothe right side in relation to the reference position (not shown).

Specifically, for example, when the steering angle to the left side orthe right side is 0 or more and less than Sθ1, a first shift amount isselected. In other words, the exposure area is set to a position that isshifted in the lateral direction by the first shift amount in relationto the reference position. When the steering angle to the left side orthe right side is Sθ1 or more and less than Sθ2 (Sθ1<Sθ2), a secondshift amount that is greater than the first shift amount is selected.When the steering angle to the left side or the right side is Sθ2 ormore, a third shift amount that is greater than the second shift amountis selected. In other words, the position of the exposure area in thelateral direction is set to a position further shifted from thereference position as the steering angle increases. In other words,detection in the traveling direction of the own vehicle becomesimportant. Here, an example is shown in which the shift amount of theexposure area is changed between three stages. However, this is notlimited thereto. The shift amount may be changed between two stages, orfour or more stages.

Next, a position of the exposure area in a vertical direction in thecaptured image based on the change amount Δθ of the pitch angle will bedescribed. As shown in FIG. 6, when the change amount Δθ of the pitchangle increases to the forward upward side (uphill direction), theposition of the exposure area in the vertical direction in the capturedimage (FIG. 6 shows exposure areas E2U and E3U) is shifted upwards inrelation to the reference position (the exposure areas E2 and E3 in FIG.4; indicated by fine lines in FIG. 6). In the example in FIG. 6, theexposure area E2U is shifted upwards in relation to the exposure area E2that is in the reference position. The exposure area E3U is shiftedupwards in relation to the exposure area E3 that is in the referenceposition. On the other hand, when the change amount Δθ of the pitchangle increases to the forward downward side (downhill direction), theposition of the exposure area in the vertical direction in the capturedimage shifts downward in relation to the reference position (not shown).

Specifically, for example, when the change amount Δθ of the pitch angleto the forward upward side or the forward downward side is 0 or more andless than Pθ1, a first shift amount is selected. In other words, theexposure area is set to a position that is shifted upwards or downwardsby the first shift amount in relation to the reference position. Whenthe change amount Δθ of the pitch angle to the forward upward side orthe forward downward side is Pθ1 or more and less than Pθ2 (Pθ1<Pθ2), asecond shift amount that is greater than the first shift amount isselected. When the change amount Δθ of the pitch angle to the forwardupward side or the forward downward side is Pθ2 or more, a third shiftamount that is greater than the second shift amount is selected. Inother words, the position of the exposure area in the vertical directionis set to a position further shifted from the reference position as thechange amount Δθ of the pitch angle increases. In other words, detectionin the traveling direction of the own vehicle becomes important. Here,an example is shown in which the shift amount of the exposure area ischanged between three stages. However, this is not limited thereto. Theshift amount may be changed between two stages, or four or more stages.

Next, the camera control section 15 calculates a control value forperforming exposure control of the camera 11 (step S104). The cameracontrol section 15 calculates the control value based on pixel values ofthe pixels included in the exposure area set at step S103. Specifically,the camera control section 15 calculates an average value (a valueindicating the brightness of the exposure area) of the pixel values(luminance values) of all pixels included in the exposure area as thecontrol value. Instead of all pixels, some pixels may be extracted asrepresentative pixels. The average value of the extracted representativepixels may be calculated as the control value. The representative pixelsmay be selected based on positions in the exposure area (for example,such that the extraction positions are not biased). Alternatively, therepresentative pixels may be selected based on color components (forexample, pixels of a certain color component among a plurality of colorcomponents). The same applies to steps S113 and S120, describedhereafter.

Next, the camera control section 15 performs exposure control of thecamera 11 based on the control value calculated at step S104 (stepS105). As a result, exposure is adjusted such as to be suitable forimaging the exposure area set in the captured image.

Next, the camera control section 15 acquires a captured image capturedafter the exposure control is performed at step S105. The camera controlsection 15 analyzes the captured image and identifies targets (accordingto the present embodiment, mobile objects, such as pedestrians,bicycles, motorcycles, and vehicles) (step S106). Identification of thetargets is performed, for example, by a matching process using targetmodels that are registered in advance. As shown in FIG. 7, theidentified targets are specified in the captured image as rectangulartarget areas (target areas T1 and T2 in the example in FIG. 7).

Next, the camera control section 15 judges whether or not a target ispresent in the captured image (whether or not a target is identified atstep S106) (step S107). When judged that a target is identified (YES atstep S107), the camera control section 15 calculates the position andthe movement direction of the target (step S108).

The position of the target (relative position to the own vehicle) can becalculated from the position of the target area in the captured image.In other words, a lower end position of the target area in the capturedimage tends to become higher as the position of the target becomesfarther in the direction ahead of the own vehicle. In the example inFIG. 7, a lower end position Y1 of the target area T1 is positionedlower than a lower end position Y2 of the target area T2. The targetarea T1 is detected to be present in a position closer to the ownvehicle than the target area T2. In this way, the distance to the targetin the direction ahead of the own vehicle can be specified based on theheight of the lower end position of the target area in the capturedimage.

In addition, a shifting of the target area in the left/right direction(specifically, a vertical line passing through the center of the targetarea) with reference to the FOE in the captured image tends to increaseas a shifting (shift in the lateral direction) of the target in anangular direction (horizontal orientation direction) with reference tothe direction ahead of the own vehicle increases. In the example in FIG.7, a shift amount X1 of the target area T1 in the leftward direction isgreater than a shift amount X2 of the target area T2 in the rightwarddirection. The shifting of the target area T1 in the angular directionwith reference to the direction ahead of the own vehicle is detected tobe greater than that of the target area T2. In this way, the horizontalorientation position of the target can be specified based on thedistance from the FOE to the vertical line passing through the center ofthe target area in the captured image. In addition, the camera controlsection 15 calculates the movement direction of the target based onchanges over time in the position of the target (displacement betweenimages captured at a predetermined cycle).

Next, the camera control section 15 judges whether or not a target ispresent in the exposure area (step S109). Specifically, in an instancein which a target area is present that at least partially overlaps withthe exposure area, the camera control section 15 judges that the targetis present in the exposure area. For example, in the example in FIG. 8,the target area T1 that partially overlaps with the exposure area E3 ispresent.

When judged that a target is present in the exposure area (YES at stepS109), the camera control section 15 resets the exposure area to anmerged area combining the exposure area and the target area thatpartially overlaps with the exposure area (step S110). In other words,the exposure area is expanded to include the target area. In the exampleshown in FIG. 8, an exposure area EU that merges the exposure area E3and the target area T1 is set.

On the other hand, when judged that a target is not present in theexposure area (NO at step S109), the camera control section 15 judgeswhether or not a target is present that does not overlap with theexposure area and is moving in a direction approaching the exposure area(specifically, a center position of the exposure area) (step S111). Whenjudged that a target that is approaching the exposure area is present(YES at step S111), the camera control section 15 resets the exposurearea to an inclusive area including the exposure area and the targetarea approaching the exposure area (step S112). In other words, theexposure area is expanded to include the target area. In the exampleshown in FIG. 9, an exposure area EI that includes the exposure area E3and the target area T1 is set. Unlike the exposure area EU (FIG. 8) towhich the exposure area is reset at above-described S110, the exposurearea EI to which the exposure area is reset at step S112 (FIG. 9)includes a connecting area that connects the original exposure area E3and the target area T1, in addition to the exposure area E2 and thetarget area T1.

In this example, to simplify the description, the judgment regarding atarget that does not overlap with the exposure area (step S111) isperformed when judged that a target is not present in the exposure area(NO at step S109). However, this is not limited thereto. For example, aplurality of targets may be detected. In this instance, targets presentin the exposure area, and targets that do not overlap with the exposurearea and are approaching the exposure area are both detected.Specifically, for example, an upper limit value (such as three targets)for the number of targets included in the exposure area (involved in theexpansion of the exposure area) is set in advance. Targets are selectedbased on order of priority such as to amount to the upper limit value orless. For example, a target that is within the exposure area and nearthe center position of the exposure area has first priority. Next, atarget that is outside of the exposure area, is approaching the exposurearea, and will reach the exposure area at an early timing has secondpriority. Here, the timing at which the target reaches the exposure areais calculated based on the movement speed at that time. Therefore, evenwhen the target is far from the exposure area, if the target isapproaching the exposure area at a high speed, the target may have ahigher order of priority than a target present near the exposure area.

When the exposure area is reset at step S110 or S112, the camera controlsection 15 calculates the average value of the pixel values (luminancevalues) of all pixels included in the reset exposure area as a controlvalue, in a manner similar to that at above-described step S104 (stepS113). However, at step S113, among the pixel values used forcalculating the control value (the pixel values of the pixels includedin the exposure area), the pixel values of the pixels included in thetarget area are weighted to have a greater influence on the controlvalue, compared to the pixel values of the pixels that are not includedin the target area. Specifically, the weight of the pixel values of thepixels included in the target area is “2”. The weight of the pixelvalues of remaining pixels is “1”. The value of the weighted average iscalculated as the control value.

Next, the camera control section 15 performs exposure control of thecamera 11 based on the control value calculated at S113 (step S114).Subsequently, the camera control section 15 proceeds to S115. Whenjudged at above-described S107 that a target is not identified (NO atstep S107) or when judged at above-described S111 that a target that isapproaching the exposure area is not present (NO at S111), the cameracontrol section 15 proceeds to step S115.

At step S115, the camera control section 15 calculates a present time Tpand an absent time Ta (step S115). The present time Tp is duration of astate in which a target is present in the captured image. The absenttime Ta is duration of a state in which a target is not present in thecaptured image. The present time Tp and the absent time Ta are measuredby a process separate from the exposure control process shown in FIG. 2and FIG. 3.

Next, the camera control section 15 judges whether or not the presenttime Tp and the absent time Ta meet a reset condition for resetting theexposure area to a reset state (step S116). Here, the exposure area inthe reset state is the exposure area having the maximum size. Accordingto the present embodiment, the exposure area in the reset state is theexposure area E1 shown in FIG. 4. In addition, according to the presentembodiment, the reset condition is that the absent time Ta continues fora second time T2 (such as three seconds) after the present time Tp hascontinued for a first time T1 (such as ten seconds). In other words, theexposure area is assumed to be reset in an instance in which, forexample, a vehicle that is traveling at a low speed on a road aroundwhich numerous targets are present, such as in an urban area, leaves theurban area and recovers traveling speed. In other words, in an instancein which a state in which a target is present changes to a state inwhich the target is not present, exposure control can be performed withthe exposure area expanded to the maximum size. As a result, theappearance of new targets to be noticed can be handled.

When judged that the present time Tp and the absent time Ta do not meetthe reset condition (NO at step S116), the camera control section 15judges whether or not the traveling speed of the own vehicle meets areset condition (step S117). According to the present embodiment, thereset condition is that the traveling speed has increased over apredetermined threshold (the traveling speed changes from a state lessthan the threshold to a state that is the threshold or more). In otherwords, as described above, the exposure area is assumed to be reset inan instance in which, for example, a vehicle that is traveling at a lowspeed on a road around which numerous targets are present, such as in anurban area, leaves the urban area and recovers traveling speed.

When judged that the traveling speed does not meet the reset condition(NO at step S117), the camera control section 15 judges whether or notan elapsed time from the start of the exposure control process shown inFIG. 2 and FIG. 3 meets a reset condition (step S118). According to thepresent embodiment, the reset condition is that a periodic reset timingis reached. The periodic reset timing is not limited to judgment basedon the elapsed time. For example, the periodic reset timing may bejudged to be reached when the number of images captured reaches apredetermined number.

When judged that the reset conditions are not met at any of steps S116,S117, and S118 (NO at step S118), the camera control section 15 returnsto step S101. On the other hand, when judged that a reset condition ismet at any of steps S116, S117, and S118 (YES at step S116, YES at stepS117, or YES at step S118), the camera control section 15 proceeds tostep S119.

At step S119, the camera control section 15 sets (resets) the exposurearea to the reset state (step S119). Next, the camera control section 15calculates a control value for performing exposure control of the camera11 based on the pixel values of the pixels included in the exposure areaset at S119 (step S120). Specifically, the camera control section 15calculates an average value of the pixel values (luminance values) ofall pixels included in the exposure area as the control value, in amanner similar to that at step S104. Next, the camera control section 15performs exposure control of the camera 11 based on the control valuecalculated at step S120 (step S121).

The camera control section 15 then judges whether or not the engine ofthe own vehicle is stopped (step S122). When judged that the engine isnot stopped (NO at step S122), the camera control section 15 returns tostep S101. On the other hand, when judged that the engine is stopped(YES at step S122), the camera control section 15 ends the exposurecontrol process shown in FIG. 2 and FIG. 3.

The target detected by the exposure control process, such as thatdescribed above, is used for vehicle control performed by the vehiclecontrol section 16 (for example, control to reduce collision based onthe position of the target). In other words, when there is a likelihoodof a collision with a target, the vehicle control section 16 transmits awarning signal to the notifying section 17 to perform notification tothe driver. In addition, when the likelihood of a collision with atarget is high, the vehicle control section 16 instructs the enginecontrol section 19 to reduce the driving force of the internalcombustion engine. In addition, the vehicle control section 16 instructsthe brake control section 18 to increase the braking force of the ownvehicle.

3. Effects

According to the embodiment that has been described in detail above, thefollowing effects can be achieved.

(1) The camera control section 15 changes the size of the exposure areain the captured image based on the traveling speed, such that the sizeof the exposure area in the captured image becomes smaller as thetraveling speed of the own vehicle increases (step S103). In otherwords, when the traveling speed is a first speed, compared to when thetraveling speed is a second speed that is lower than the first speed,the size of the exposure area in the captured image is set to besmaller.

Therefore, according to the present embodiment, the exposure area can beset to a size suitable for the traveling speed of the own vehicle. Inother words, as shown in FIG. 10, with reference to a fixed collisionmargin time TTC, the distance to a subject obstacle becomes farther asthe traveling speed of the own vehicle increases. Therefore, in asituation in which the traveling speed is high, compared to a situationin which the traveling speed is low, importance is required to be placedon the detection of targets at a farther distance. According to thepresent embodiment, when the traveling speed is high, the exposure areain the captured image is set to be small in size. Therefore, importancecan be placed on the detection of targets at a far distance.

(2) The camera control section 15 identifies a target area that is anarea in which a target is present in the captured image (step S106). Thecamera control section 15 weights the pixel values of the pixelsincluded in the target area, among the pixels included in the exposurearea, compared to the pixel values of the pixels not included in thetarget area, such that the influence on the control value is greater(step S113). Therefore, according to the present embodiment, compared toan instance in which the pixel values are not weighted, exposure controlthat places importance on the imaging state of a target can beactualized.

(3) In an instance in which a target area is present that partiallyoverlaps with the exposure area set based on detection information(travel conditions of the own vehicle), the camera control section 15expands the exposure area to include the target area (step S110).Therefore, of the target area that partially overlaps with the exposurearea, pixel values of pixels included in a portion not overlapping withthe exposure area can also be used for calculation of the control value.As a result, according to the present embodiment, compared to aninstance in which the exposure area is not expanded, exposure controlthat places importance on the imaging state of a target can beactualized.

(4) In an instance in which a target area is present that does notoverlap with the exposure area set based on detection information(travel conditions of the own vehicle) and is approaching the exposurearea, the camera control section 15 expands the exposure area to includethe target area (step S112). Therefore, pixel values of pixels includedin a target area that does not overlap with the exposure area can alsobe used for calculation of the control value. As a result, according tothe present embodiment, compared to an instance in which the exposurearea is not expanded, exposure control that places importance on theimaging state of a target can be actualized.

(5) The camera control section 15 changes the position of the exposurearea in the lateral direction in the captured image based on thesteering angle (step S103). Therefore, according to the presentembodiment, compared to an instance in which the position of theexposure area in the lateral direction in the captured image is fixedregardless of the steering angle, the exposure area can be set in asuitable position based on the steering angle.

(6) The camera control section 15 changes the position of the exposurearea in the vertical direction in the captured image based on the pitchangle (step S103). Therefore, according to the present embodiment,compared to an instance in which the position of the exposure area inthe vertical direction in the captured image is fixed regardless of thepitch angle, the exposure area can be set in a suitable position basedon the pitch angle.

(7) In an instance in which a predetermined reset condition is met, thecamera control section 15 resets the size of the exposure area in thecaptured image to a reset state (step S119). The camera control section15 then calculates the control value based on the pixel values of thepixels included in the reset exposure area (step S120). Therefore,according to the present embodiment, compared to an instance in whichthe size of the exposure area in the captured image is not reset to thereset state, tracking of changes in the travel conditions of the ownvehicle and the like can be facilitated.

(8) The camera control section 15 uses the following as a resetcondition: after a state in which a target is present in the capturedimage (present time Tp) continues for a first amount of time, a state inwhich a target is not present in the captured image (absent time Ta)continues for a second amount time (step S116). Therefore, according tothe present embodiment, the size of the exposure area can be reset tothe reset state when a state in which a target is present changes to astate in which the target is not present. In addition, becausecontinuation of the time is a condition, a phenomenon in which resetfrequently occurs in a situation in which a target frequently appearsand disappears is unlikely to occur.

(9) The camera control section 15 uses the following as a resetcondition: the traveling speed of the own vehicle increases over apredetermined threshold (step S117). Therefore, according to the presentembodiment, the size of the exposure area can be reset to the resetstate when a state in which the own vehicle should travel at a low speed(such as when a target is present) changes to a state in which the ownvehicle can travel at a high speed (such as when no targets arepresent).

(10) The camera control section 15 uses the following as a resetcondition: a periodic timing is reached (step S118). Therefore,according to the present embodiment, a phenomenon in which the size ofthe exposure area is not reset for a long period of time is unlikely tooccur.

According to the present embodiment, the camera control section 15 isequivalent to an example of the exposure control device. Step S101 isequivalent to an example of processing as an image acquiring means. StepS102 is equivalent to an example of processing as a speed acquiringmeans, a steering angle acquiring means, and a pitch angle acquiringmeans. Step S103 is equivalent to an example of processing as a settingmeans. Steps S104, S113, and S120 are equivalent to an example ofprocessing as a calculating means. Step S106 is equivalent to an exampleof processing as an identifying means. Step S110 is equivalent to anexample of processing as a first expanding means. Step S112 isequivalent to an example of processing as a second expanding means. StepS119 is equivalent to an example of processing as a reset means.

4. Other Embodiments

An embodiment of the present invention is described above. However, thepresent invention is not limited to the above-described embodiment.Various embodiments are possible.

(1) According to the above-described embodiment, a configuration exampleis described in which a plurality (upper limit value or less) of targetsare selected based on order of priority as target areas involved inexpansion of the exposure area (target areas partially overlapping withthe exposure area or target areas approaching the exposure area).Specifically, an example is described in which a target that is withinthe exposure area and near the center position of the exposure area hashigher priority. A target that is outside of the exposure area, isapproaching the exposure area, and will reach the exposure area at anearly timing has lower priority. However, such order of priority ismerely an example. Other orders of priority may also be used. Forexample, a target having a short collision margin time TTC may havehigher priority. A target that will reach, at an early timing, aposition (lower end position) in the exposure area at which thecollision margin time TTC is the shortest may have lower priority. Ashort collision margin time TTC indicates that the distance in thedirection ahead of the own vehicle is short, and that the lower endposition of the target area is low. In the example in FIG. 11, thetarget area T1 of which the lower end position is the lowest (thecollision margin time TTC is about 1.5 seconds) has the highestpriority. Next, of the target areas T2 and T3 of which the lower endpositions follow the target area T1 in terms of shortness (the collisionmargin time TTC is about 2 seconds), the target area T3 that is movingtowards the own-vehicle side has the second highest priority.

(2) According to the above-described embodiment, a configuration isgiven as an example in which the weight of the pixel values of thepixels included in the target area is 2. The weight of the pixel valuesof remaining pixels is 1. A weighted average is then calculated (stepS113). However, the present invention is not limited thereto. Forexample, the weighting coefficient may be set to other values. Inaddition, for example, the weight of the pixel values of pixels includedin the target area may differ based on the type of target area.Specifically, compared to the pixel values of a target moving in adirection away from the center of the exposure area, the pixel values ofa target moving in a direction towards the center of the exposure areamay be weighted to have a greater influence on the control value. As aresult, exposure control that places importance on the imaging state ofa target having a high risk of collision can be actualized.

(3) According to the above-described embodiment, three reset conditionsfor resetting the exposure area to the reset state are given as examples(Steps S116 to S118). However, the present invention is not limitedthereto. For example, one or two of the three reset conditions may beused. Alternatively, a reset condition other than the three resetconditions may be used.

(4) According to the above-described embodiment, the position of theexposure area in the captured image is changed depending on the steeringangle and the pitch angle of the own vehicle. However, the presentinvention is not limited thereto. For example, the shape of the exposurearea (such as width and height) may be changed.

(5) According to the above-described embodiment, a rectangular exposurearea is given as an example. However, the shape, position, size, and thelike of the exposure area are not particularly limited.

(6) According to the above-described embodiment, a configuration inwhich the pitch angle is detected by the gyro sensor 14 is given as anexample. However, the present invention is not limited thereto. Forexample, the pitch angle may be detected using an acceleration sensor oran inclinometer.

(7) According to the above-described embodiment, notification control,brake control, and engine control are given as examples of vehiclecontrol. However, the present invention is not limited thereto. Forexample, the steering angle and the like may be controlled. In addition,the vehicle control is not limited to control for reducing collisionsand may be other types of control.

(8) According to the above-described embodiment, mobile objects, such aspedestrians, bicycles, motorcycles, and vehicles, are given as examplesof the target. However, the present invention is not limited thereto.Other types of targets may be detected.

(9) The constituent elements of the present invention are conceptual andare not limited to the above-described embodiment. For example, afunction provided by a single constituent element may be distributed toa plurality of constituent elements. Alternatively, functions providedby a plurality of constituent elements may be integrated in a singleconstituent element. At least a part of the configuration according tothe above-described embodiment may be replaced by a known configurationhaving similar functions. Moreover, at least a part of the configurationaccording to the above-described embodiment may, for example, be addedto or replace, the configurations in the other embodiments describedabove.

What is claimed is:
 1. A device for controlling exposure of a camera,comprising: means for acquiring an image of an area ahead of a vehicleby a camera provided in the vehicle; means for acquiring a travelingspeed of the vehicle; means for setting an exposure area in the acquiredimage, the exposure area being an area used for exposure control of thecamera; means for calculating a control value for performing theexposure control of the camera, based on pixel values of pixels includedin the exposure area, wherein the setting means changes a size of theexposure area in the acquired image based on the traveling speed, suchthat, when the traveling speed is a first speed, the size of theexposure area in the acquired image is smaller compared to that when thetraveling speed is a second speed that is lower than the first speed. 2.The device of claim 1, comprising means for identifying a target area inthe acquired image, a target being present in the target area, whereinthe calculating means includes means for weighting the pixels of theexposure area such that pixels included in the target area which arestill included in the exposure area have a larger influence on thecontrol value compared with that of pixels which are outside the targetarea.
 3. The device of claim 2, comprising first means for determiningwhether or not the target area is partially overlapped with the exposurearea; and first means for expanding the exposure area such that theexposure area includes the target area when the first determining meansdetermines that the target area is partially overlapped with theexposure area.
 4. The device of claim 3, comprising second means fordetermining whether or not the target area is overlapped with theexposure area, but moves toward the exposure area; and second means forexpanding the exposure area such that the exposure area includes thetarget area when the second determining means determines that the targetarea is not overlapped with the exposure area, but is moving toward theexposure area.
 5. The device of claim 4, comprising means for acquiringa steering angle of the vehicle, wherein the setting means includesmeans for changing a lateral position of the exposure area in theacquired image depending on the acquired steering angle.
 6. The deviceof claim 5, comprising means for acquiring a pitch angle of the vehicle,wherein the setting means includes means for changing a verticalposition of the exposure area in the acquired image depending on theacquired pitch angle.
 7. The device of claim 6, comprising third meansfor determining whether or not a reset condition predetermined for asize of the exposure area in the acquired image is met; and means forresetting the size of the exposure area into a so predetermined initialsize of the exposure area, wherein the calculating means calculates thecontrol value based on values of pixels included in the exposure areawhich has been reset.
 8. The device of claim 2, comprising second meansfor determining whether or not the target area is overlapped with theexposure area, but moves toward the exposure area; and second means forexpanding the exposure area such that the exposure area includes thetarget area when the second determining means determines that the targetarea is not overlapped with the exposure area, but is moving toward theexposure area.
 9. The device of claim 8, comprising means for acquiringa steering angle of the vehicle, wherein the setting means includesmeans for changing a lateral position of the exposure area in theacquired image depending on the acquired steering angle.
 10. The deviceof claim 9, comprising means for acquiring a pitch angle of the vehicle,wherein the setting means includes means for changing a verticalposition of the exposure area in the acquired image depending on theacquired pitch angle.
 11. The device of claim 10, comprising third meansfor determining whether or not a reset condition predetermined for asize of the exposure area in the acquired image is met; and means forresetting the size of the exposure area into a predetermined initialsize of the exposure area, wherein the calculating means calculates thecontrol value based on values of pixels included in the exposure areawhich has been reset.
 12. The device of claim 1, comprising means foracquiring a steering angle of the vehicle, wherein the setting meansincludes means for changing a lateral position of the exposure area inthe acquired image depending on the acquired steering angle.
 13. Thedevice of claim 1, comprising means for acquiring a pitch angle of thevehicle, wherein the setting means includes means for changing avertical position of the exposure area in the acquired image dependingon the acquired pitch angle.
 14. The device of claim 1, comprising thirdmeans for determining whether or not a reset condition predetermined fora size of the exposure area in the acquired image is met; and means forresetting the size of the exposure area into a predetermined initialsize of the exposure area, wherein the calculating means calculates thecontrol value based on values of pixels included in the exposure areawhich has been reset.
 15. The device of claim 14, wherein the resetcondition is defined as a condition that a first period of time during atarget is present in the acquired image lasts, and then a second periodof time a target is not present in the acquired image lasts.
 16. Thedevice of claim 14, wherein the reset condition is defined as acondition that the traveling speed of the vehicle increases to cross agiven threshold thereof.
 17. The device of claim 14, wherein the resetcondition is defined as a condition that time advances to regularly setreset timing after start of the exposure control.
 18. A method ofcontrolling exposure of a camera, comprising steps of: acquiring animage of an area ahead of a vehicle by a camera provided in the vehicle;acquiring a traveling speed of the vehicle; setting an exposure area inthe acquired image, the exposure area being an area used for exposurecontrol of the camera; and calculating a control value for performingthe exposure control of the camera, based on pixel values of pixelsincluded in the exposure area, wherein the setting step changes a sizeof the exposure area in the acquired image based on the traveling speed,such that, when the traveling speed is a first speed, the size of theexposure area in the acquired image is smaller compared to that when thetraveling speed is a second speed that is lower than the first speed.